1. Field of the Invention
The present invention generally relates to a wafer polishing method, in particular, to a wafer polishing method capable of preventing wafer cracks.
2. Description of Related Art
Microelectromechanical system (MEMS) is a microelectromechanical component fabricated in a microminiaturized package structure, and the fabricating technique thereof is quite similar to the technique of fabricating integrated circuits (ICs). However, interactions, for example, about mechanics, optics, or magnetic force between the MEMS device and surrounding environment are more than that of the conventional IC.
The MEMS device may include micro-sized electromechanical components (for example, switches, mirrors, capacitors, accelerometers, sensors, capacitive sensors, or actuators etc.), and the MEMS device may be integrated with the IC in a manner of single block, thereby greatly modifying insertion loss or electrical isolation effect of the overall solid-state device. However, in the macroscopic world of the entire package structure, the MEMS device is extremely weak and may be impacted by slight static electricity or surface tension at any moment to cause failure. Therefore, in order to prevent the MEMS device from contaminations or damages, usually the MEMS device is sealed in a cavity of the wafer.
FIG. 1 is a schematic view of cracks generated in a conventional wafer polishing process. Referring to FIG. 1A, the wafer 100 has a plurality of lattice opening portions 102 (or cavities). However, in the polishing process, since the strength at regions A and B becomes weak, the regions A and B (for example, the edges) of the wafer are usually cracked, and silicon residue 104 easily clogs the opening portions 102. Therefore, the present invention is mainly directed to overcome serious defects such as cracks and residues occurred in the polishing process.